The invention relates to cathode ray tubes and more particularly to a low power cathode assembly for such a tube in which thermal losses due to heat conduction along the cathode sleeve and radiation losses from the cathode sleeve are reduced.
U.S. Pat. No. 2,914,694, issued to T. N. Chin on Nov. 24, 1959, describes a low power cathode for an electron discharge device. A cathode sleeve is supported by a funnel-shaped member made of a material, such as a cobalt-nickel-iron alloy, having low heat conduction properties to minimize heat loss to the other cathode support structures. A cathode shield, also made of the same low heat conduction property material, surrounds and supports the funnel-shaped member. The funnel-shaped member and the cathode shield are provided with bright inner surfaces to reflect as much heat as possible back toward a cathode cap.
U.S. Pat. No. 4,370,588, issued to Takahashi et al. on Jan. 25, 1983, discloses a low power cathode having a cathode sleeve which is blackened to uniformly radiate heat. A first cylindrical reflective member surrounds the upper portion of the cathode sleeve and reflects heat from the cathode sleeve to reduce heat radiation to the outside. A second cylindrical reflective member supports the cathode sleeve on three support members. The inner surface of the second reflective member also reflects some of the heat from the lower portion of the cathode sleeve so that it is not radiated to the outside in order to provide a power savings. However, the openings between the support members permit some heat to be lost.
The aforementioned cathode structures each comprise a number of parts which require careful and costly assembly steps. Therefore, there is a need for a simple cathode structure that provides both low thermal conduction and low radiation losses.